Process for recovering chemicals from aqueous soap solutions



Aug. 5, 1958 D. B. MAPES ET AL 2,846,460

PROCESS FOR RECOVERINC CHEMICALS FROM AQUECUS SOAP SOLUTIONS Filed March 8, 1956 ALCOHOLS DWIGHT B. MAPES TRUMAN P. MOOTE,JR.

A T TOR/VE Y United States Patent O PROCESS FOR RECOVERING CHEMICALS FROM AQUEOUS SOAP SOLUTIONS Dwight B. Mapes and Truman P. Moote, Jr., Tulsa, Okla., assignors to Pan American Petroleum Corporation, a corporation of Delaware Application March 8, 1956, Serial No. 570,237

6 Claims. (Cl. 260-450) The present invention relates to a method for the recovery of various oxygenated organic chemicals from solutions thereof. More particularly, it pertains to a process for recovering in substantially pure form a relatively high percentage of oil soluble alcohols from crude hydrocarbon or other mixtures containing carbonyl compounds,

While the principles taught herein iind application in the recovery of chemicals from numerous kinds of crude mixtures, the present description deals particularly With the problems encountered in recovering valuable chemicals from the oil stream produced by the hydrogenation of carbon monoxide in the presence of a fluidized alkalipromoted iron catalyst under known synthesis conditions. This oil fraction obtained in the hydrocarbon synthesis process, contains a rather Wide variety of acids, carbonyl compounds (ketones and aldehydes), and alcohols together with a small proportion of esters. For example, in hydrocarbon synthesis plants designed to produce approximately 640,000 lbs. per day of liquid hydrocarbons, there are simultaneously produced along with this oil fraction 108,000 lbs. of oil soluble carbonyl compounds, 93,000 lbs. of oil soluble alcohols, 32,000 lbs. of esters, and 83,000 lbs. of oil soluble acids. Owing to their value as chemicals, it is desirable to separate these compounds from the oil stream as completely as possible. Also in the subsequent conversion of the aforesaid oil fraction into gasoline, it is imperative that such compounds either be removed from the oil or converted into substances such as, for example, unsaturated hydrocarbons, which can then be utilized in conjunction with the hydrocarbons originally synthesized to make high quality motor fuels.

Because of the proximity in boiling points of these various oil soluble chemicals to the hydrocarbons constituting the oil fraction, separation of chemicals from hydrocarbons by normal fractional distillation methods is a practical impossibility.

In recovering oil soluble chemicals 'from hydrocarbon solutions thereof, it has been proposed that soap solutions of various types be employed as selective solvents or extractants for such chemicals. Generally, these soap solutions are not composed of soaps in the true sense, but are made up largely of substantially non-surfaceactive salts of alkali metals or their equivalent salts derived from carboxylic acids having an average molecular Weight ranging from about 85 to about 135. Soap solutions of this type are most conveniently prepared by adding the required amount of caustic or other suitable base to the primary oil fraction produced in hydrocarbon synthesis whereby the free acids present in said fraction are neutralized. By agitation of the resulting mixture, a substantial portion of the oil-soluble chemicals present therein tend to pass into the lower aqueous layer. Along with the chemicals dissolved in the' soap solution, there is usually found from about to 10 Weight percent of hydrocarbons solubilized therein. The latter, generally speaking, are undesirable because they tend to impart objectionable characteristics to the chemicals recovered from such solutions. ASeparation of the hydrocarbons from the ICC 2 chemicals has been `a relatively diflicult job since the former vboil over substantially the same range as the chemicals, making ordinary distillation separation methods of little value.

In practice, primary oil from hydrocarbon synthesis was first mixed with suicient caustic to neutralize the free acids in the oil, the resulting soaps forming a lower aqueous phase which separated from the neutral oil. The neutral oil was next extracted with a lean soap solution of the type hereinafter dened and the resulting extract, which contained oxygenated chemicals and solubilized hydrocarbons, was combined with the chemical-rich soap solution formed in the above-mentioned neutralization step. These combined streams Were then subjected to extraction with a light hydrocarbon (hereinafter referred to as deoiling or the deoiling step) such as for example, liquid propane or liquid butane, for the purpose of removing from the soap solution any hydrocarbon dissolved by the soap in the neutralization and extraction steps. The ra'inate from this extraction consisted chiefly of an oil-free soap solution containing oil-soluble oxygenated organic chemicals and Was thereafter fractionated under pressure to separate any light hydrocarbon solvent present after which the soap solution was stripped free of chemicals in a conventional fractionating still. The light hydrocarbon extract obtained from the deoiling step contained both high molecular weight hydrocarbons and relatively high molecular weight chemicals, particularly ketones and esters, and was generally sent to a flash drum or to a distillation unit Where the butane was removed overhead and returned to the deoiling step. The bottoms from the butane recovery step consisted principally of hydrocarbons and chemicals and was recycled and combined with the neutral oil feed to the soap extraction step. Under such conditions, however, a rather substantial buildup of chemicals, chiefly high molecular Weight ketones and esters, occurred in the soap extractor requiring higher soap to oil ratios to remove these chemicals. Owing to the use of such higher oil to soap ratios, the quantity of dissolved hydrocarbons in the resulting extract increased, thereby requiring increased amounts of butanein the deoiling operation. In other words, it was found that larger and larger quantities of light hydrocarbon extractant were required to produce a rich soap extract which contained a minimum concentration of hydrocarbons. To avoid this diiculty, the bottoms from the butane recovery step containing an appreciable quantity of chemicals was withdrawn from the system and either discarded therefrom or separately processed to recover the chemicals and hydrocarbons as individual fractions.

Accordingly, it is an object of our invention to provide a process whereby the chemicals in a hydrocarbon solution thereof can be substantially completely recovered free of hydrocarbon contaminants. It is another object of our invention to effect a further separation of carbonyls and/ or esters from alcohols present in said hydrocarbon solutions to give a fraction of such alcohols substantially free from both hydrocarbons, carbonyls and/or esters. Another object of our invention is to recover a substantially pure alcohol fraction from an aqueous solution comprising alcohols, carbonyls and dissolved hydrocarbons in contaminating amounts, by contacting said solution with a liquid light saturated hydrocarbon under controlled conditions of temperature, pressure and volume ratios of said light hydrocarbon to said aqueous solution to selectively extract said contaminating hydrocarbons and carbonyls in separate extraction steps from said aqueous solution to yield a solution of alcohols substantially free of hydrocarbons and carbonyls.

Brietly we accomplish the above and other objects of our invention by controlling both the temperature of the light hydrocarbon employed to decil the original soap 3 i extract and the volume lratio of light hydrocarbon to aqueous soap extract employed.

In carrying out the process of our invention the conditions employed in -the rst-extraction step should be closely controlled in order to obtain the desired results. Thus to achieve the required selectivity, extraction of contaminating hydrocarbons by means of a liquid-.light hydrocarbon should be effected at a volume ratio of liquid light hydrocarbon to soap extract ranging VVfrom 'about 1:10 to about 1:4. With these volume ratios temperatures from above 80 F. up to slightly below, i. e. about 5 below, the critical temperature ofthe lighthydrocarbon may be'employed. In the case Yof propane the preferred extraction temperature ranges from about 140 to about 180 F. while temperatures ranging from about 160 to about 200v F. are considered most desirable for the butanes. At temperatures in the range of 80F. and below, the selective solvent power of propane decreases substantially causing increasing Vamounts of chemicals to be extracted from `the soap along with dissolved hydrocarbons. VThis particular extraction step is preferably carried out under conditions such that a single stage of contacting between the solvent and the soap extract occurs. With more than two extraction stages the quantity of chemicals extracted with the contaminating hydrocarbons becomes substantial. Accordingly, this rstextraction step should be conducted in a short extraction zone in .whichronly one or two'stages of contact are favored.

In this connection the terms single stage or single extraction stage, as used 'in the present description and claims, is intended to refer to a condition produced or prevailing within an extraction column wherein a given volume of solvent is used to extract a xed volume of feed to yield rainate and extract phases corresponding lto those resulting from a batch extraction where solvent and feed are permitted to reach equilibrium. When the expressions multi-stage extraction or multi-stage extractor are used such terms `are intended to refer toa plurality ofV extraction 'stages in a column in which'the solvent countercurrently contacts the feed-to be extracted. In a case of this'ltype a five stage extraction would be dened as a system havingve different equilibrium stages or the equivalent thereof, in which thesolvent and the feed are countercurrently contacted.V Multi-stage extraction in carrying out the second extraction step ofour invention is desirable, with equipment providing forfrom live to ten extraction stagesv generally being preferred.

An Vadditional factor to be considered in the frst extractionstep, i. e. the step in which only dissolved hydrocarbons are removed from the soap extract, is that lower volume ratios of light hydrocarbon solvent to soap are required to yremove dissolved hydrocarbons from selected soap solutions, the latter constituting alkali metal or equivalent salts of C2 to C6 aliphatic carboxylic acids. Lower volume ratios of light hydrocarbon solvent'toY soap are required in the above instance because extracts obtained by the use of such soap solutions generally contain less contaminating hydrocarbons and such hydrocarbons are more readily removed. On the otherhand with soap solutions of the higher molecularweight soaps, i. e. -those prepared from carboxylic acids having an averagemolecular weight of from about 125 to about 135, higher vol-V ume ratios of solvent to soap extract are ordinarily needed because such soaps extract larger amounts of hydrocarbons from the HCS oil and such hydrocarbons are more diicult to selectively remove from soap extracts Vof this type.

Pressures 'which may be employed in the rst-mentioned extraction step range from a vminimum of about 140 p. s. i. for propane ata temperature of Vabout 80 to 85 F. to a practical maximum of about 500.p. s. i., with pressures in the range of 300 to 400. p. s. i. being preferred at temperatures in the range of 140 to 180 F. Higher pressures, of course, may be used, however, the advantage tolbe gained atvpressures in excess Vof 500 p. s. i.'tend to be overcome rather rapidly by increased compression costs. Minimum pressures for the butanes when used in this same step are in the neighborhood of 25 to 50 p. s. i. at temperatures of 80 to 85 F. However, when using the butanes as the light hydrocarbon extractant temperatures of the orderof 160 to 200 F. are ordinarily preferred, using pressures in the range of from about 125 to about 235 p. s. i.

In the second 'extraction step the minimum pressures for propane'range from about 115 to about 140 p. s. i. at temperatures of from 65 to 85 F. Corresponding pressures for the butanes over the same temperature range vary from about 20 to about 50 p. s. i.

The expression carbonyls, as used herein, is intended to cover esters as wellas ketones and alde'hydes.

After dissolved hydrocarbons have ben removed from the soap by means of the first extraction step the hydrocarbon-depleted soap extract is. next -countercurrently extracted with liquid light hydrocarbonk in volume ratios-of light hydrocarbon to soap ranging from about .5:1 to about 2:1 at temperaturesV of vfrom about 65 to about F. For both propane and the butanes the preferred temperature is in the neighborhood of from 70 to 80 F. while the pressures employed over this range may vary from about to about 135 p. s. i.

Soap solutions employed to obtain the extracts used as feed in the process of our invention may range in ,concentration of fromfabout 20 to 50 weightpercent. With concentrations above 50 weight percent some diiiculty is encountered owing -to the fact Vthat at such concentrations the soap tends to form a gel. With soap solutions of 50 weight percent or less gels are produced when using pen-' tane or'high molecular weight solvents due to the solu- -bility of the soap in the higher hydrocarbons. Accordingly, we desire to restrictthe light hydrocarbon solvents usedin our process to propane andthe butanes, propane generally being preferred. n

The process of our invention may be described in further detail by reference to thev accompanying ow diagram wherein, `for example a chemically rich soap extract resulting from the extraction of a neutral HCS oil with a lean aqueous soap'solution is fedinto the upper portion of a single stage extraction column 2 through line 4. Countercurrently, liquid propane at a pressure of 325 p. s. i. is introduced through line 6, at 'a lower level, into column 2. The temperature within the extraction zone is about F., the pressure being inthe neighborhood of about 325 p. s. i. lOverhead through line -8 an extract of hydrocarbons from the aforesaid rich soap phase -dissolved `in propane is withdrawn. The quantity of hydrocarbons in .the propane extract represents all of `said hydrocarbons present inthe original-'ex-` tract fed to the column. Only a relatively small percent-y age of the chemicalsis taken overhead with the stream in line 8. Said stream after being reduced inpressure to about200 p. s. i. by means of valve 10 is next sent to column 12,'operated at a bottoms temperature ofabout 150 F., where a mixture of hydrocarbons is removed through line 14. Overhead propane vapors, at 200 lbs. pressure, `are taken ol `through `line 16, cooled injcondenser 18 to a temperature of about 75 VF. and'then sent to liquidpropane storage :tank 20 whichV is maintained at'about 200 p. s. i. The hyrocarbons in line 14 are sent to column 22 operated at a bottoms temperature of 1150" F. The pressure on this mixture is reduced to atmospheric by means of valve Y24 priorto enteringcolumn 22. VIn

this column 'propane is taken off overhead through llinel soap extract containing carbonyls and alcohols. This stream, after being cooled to about 75 to 80 F. in cooler 36 and reduced in pressure to about 200 p. s. i. by means of valve 38, is next transferred to a multi-stage extraction column 40 where it is introduced at an upper portion thereof and is countercurrently contacted by a liquid stream of propane, introduced through line 42 and transferred therethrough from storage tank 20 by means of pump 44. The temperature within the extraction zone of column 40 is maintained at 75 to 80 F.

Although the pressure required to hold the propane in the liquid phase Within the aforesaid temperature range varies |from about 125 to about 150 p. s. i., we prefer to employ a pressure of about 200 p. s. i. at this stage in order to maintain ow of overhead from column 40 through subsequent portions of the system. The quantity of propane introduced into the system is such as to give a volume ratio of propane to aqueous soap solution introduced through line 34 of about 1:1. Overhead the resulting propane extract is withdrawn through line 46 and contains substantially all of the carbonyls and/or esters and a portion of the alcohol present in the original charge to column 2 leaving an aqueous soap solution containing alcohols, but substantially free from carbonyls, to be withdrawn through line 48. The stream in line 48 is next sent to stripping column 50 where it is introduced into an upper portion thereof. Within this column separation of the aqueous and organic (alcohol) phases is eiected with the concentrated soap phase being withdrawn as bottoms through line 52, where it may be further pun'ed if desired or used without further purification in a subsequent extraction of neutral HCS oil to provide additional feed for column 2. The overhead Ifrom column 50 is withdrawn through line 52 and condenser 54 and allowed to stratify in separator 56. The water layer is returned to the stripping column as reflux through line 58 While the upper organic layer, consisting essentially of product alcohols, is withdrawn through line 60.

The overhead from column 40 passes through ow control valve 62 and thereafter is introduced into column 64 operated at a bottoms temperature of about 150 F. and at a pressure of about 200 p. s. i., i. e., the pressure corresponding to the vapor pressure prevailing in storage tank 20 which may range from about 140 to about 200 p. s. i. Gaseous propane at 200 p. s. i. is taken olf through line 66 and combined with propane in line 16. The bottoms, consisting chiey of carbonyls and some alcohols together with a small amount of propane is then transferred through line 68 and pressure relief valve 70 to column 72. Column 72 is operated at atmospheric pressure and at a temperature of about 150 F. A liquid propane reux is supplied to the column through line 74 supplied by line 6. Carbonyls together with some alcohols are withdrawn from the bottom of column 72 through line 76. Under the conditions of operation all of the propane in column 72 passes out the top thereof through line 78 where it joins propane also at atmospheric pressure in line 80. These combined streams then pass through line 80 and into line 26. This gas is next passed through compressor 28 and delivered into line 16 at a pressure of about 200 p. s. i.

The ability of the process of our invention to separate hydrocarbons and carbonyls from soap extracts of the above mentioned type, leavinga soap solution of substantially pure alcohols, is further illustrated by the following speciic example.

Example About 800 cc. of an extract comprising a 50 weight percent aqueous soap solution and oil soluble alcohols (0.430 g. mol) and carbonyls (0.222 g. mol) together with contaminating hydrocarbons obtained by extraction of a nonacidic HCS oil fraction is subjected to a single stage extraction step with about 200 cc. of liquid propane at a temperature of about 150 F. and at a pressure of about 340 p. s. i. initial extract (feed) is derived from aliphatic acids having an average molecular weight ranging from about to about 135. In this extraction step approximately 98 to 100 weight percent of the contaminating hydrocarbons dissolved in the soap extract are removed. The rainate from the last extraction is next subjected to further treatment in a tower having live extraction stages. At a point near the base of this tower liquid propane is added at a rate such that the volume ratio of propane to soap extract is about 1:1. Within the extraction zone the temperature is maintained at about 75 F. and the pressure employed is about p. s. i. Under these conditions a rising stream of propane removes from a descending charge of soap extract about 97 mol percent of the carbonyls and about 45 mol percent of the alcohols. Total chemicals extracted from the initial feed amounts to about 75 mol percent. The extracted stream of chemicals, however, on separation can be subjected to mild hydrogenation in accordance with known conditions to produce a mixture of secondary and primary alcohols free from hydrocarbons. After the second extraction step the soap solution contains approximately 55 mol percent of the alcohols present in the original soap extract. Such soap solution is free from hydrocarbons and contains no more than about 3 mol percent of the carbonyls originally present.

One of the outstanding features of the process of our invention is the fact that we are able to secure a highly puriied fraction of primary product alcohols. This fact is important because in the use of such alcohols such as, for example in the manufacture of plasticizers it is desired that the plasticizers be free from both hydrocarbons and reaction products of secondary alcohols. Experience has shown that materials containing plasticizers having such impurities therein, tend to discolor on exposure or aging. Plasticizers made from primary alcohols of the type recovered in the process of our invention, however, have been found to retain good color and plasticizing properties over extended periods.

From the foregoing description and example, it is apparent that the process of our invention atords a con- Venient method for recovering oil soluble alcohols in highly purilied form from complex mixtures containing close boiling hydrocarbons and carbonyl compounds, Our invention, therefore, in its broadest aspect, contemplates accomplishing the above results by controlling, within relatively narrow limits, the temperature, pressure and the volume ratio of solvent to feed.

We claim:

1. In a process for the recovery of a substantially pure alcohol fraction from a 20 to 50 weight percent aqueous carboxylic acid soap solution comprising carbonyls and alcohols of the type found in the hydrocarbon phase produced by the Fischer Tropsch synthesis and contaminating amounts of dissolved hydrocarbons, said soap being derived from a mixture of fatty acids having an average molecular weight ranging from about 85 to about 135, wherein said soap solution is contacted with a liquid light saturated hydrocarbon having from 3 to 4 carbon atoms, the improvement which comprises iii-st extracting said soap solution with said light hydrocarbon in a volume ratio of light hydrocarbon to said solution of from about 1:10 to 1:4 at a temperature ranging from about 80 F. to not more than about 5 F. below the critical temperature of said light hydrocarbon and at minimum pressures ranging from about 25 to 50 p. s. i. for the C4 hydrocarbons to about 140 p. s. i. for the C3 hydrocarbon, said extraction being carried out in an extraction zone of not more than about one stage, thereafter subjecting the rainate from said extraction, which rafnate is now substantially free from contaminating hydrocarbons, to a second extraction step in a multi-stage extraction zone having not more than about ten stages, wherein said raflinate is extracted with a liquid The soap employed in securing the volume'ratio of saidflight hydrocarbon to saidra'nate rangingfrom about .5:'1 to about 2:1, at a` temperaturev of from about 65 to about 85 1:".y and at .a minimum pressureof from about 115 to about 140 vp. s. i. for the C3 hydrocarbon and from about 20 to about 50 p. s. i. for the C4 hydrocarbonto yield a raffinate containing alcohols substantially free of said contaminating hydrocarbons and carbonyl compounds. i Y

2. The process of claim Y1 in which liquid propane is employedV as `the liquid light hydrocarbon, the temperature employed Vin the rst extraction stepis from about 140 to about 180 F. -and .the `temperatureat which' said second extractionstepis .carriedout is from about 70L to about 80 Ff 3. The process 'of clajmd in which n-butane is ernployed .as Vthe liquid light hydrocarbon, the temperature employed in the rst extaction step is from about 160 toabout 200 F. and the temperature at which said second extraction step is carried out is vfrom about 70 to 80 F. with pressures in the rst extraction step being at a minimum of 125 p. s.. i., at 160 F., and ata minimum of 235 p. s. i.,- at 200 F., and pressures in the second step being at a minimum of about 25 p. s. i. v

4. The process of claim 1 in which a C4 hydrocarbon is employed as the liquid light hydrocarbon and the minimum pressures in both extraction steps range from 25 to about 50 p. s. i.

5. The `process of: claimY 4u in. which ,the liquid ,iight hydrocarbonis n-butane. Y

6. Ina process for the recovery ofa ,substantially pure alcohol fraction from a 20 to 50 Weight percentaqueous soap solution free. from contaminating hydrocarbonsgbut containing. alcohols and carbonyl compounds of the type'y found in the hydrocarbon .phase produced by the Fischer A Tropsch synthesis, said soap being derived from' a'mixture offatty acids havingnaverageV` molecular Weight ranging.

from about 85 to about 135, the improvement which comprises subjecting said soap solution-.to .extraction in a multi-stage extraction zone having not more thanabout ten stages, wherein said soap solution is extracted with a liquid light hydrocarbon having vfrom 3 to`4carbonratoms,

the volumeratio of `said lightv hydrocarbon lto said soap' solution ranging from about 5 :1 to about 2:1, Vat. a temfor the C3 hydrocarbon and from about 20 to about 50 p. s. i. for the C4 hydrocarbon, yto yield a ralinate containing alcohols substantially free of said carbonyl coml pounds.

References Cited in the file of this patent UNITED STATES PATENTS McGrath Feb. 27, 1951 Grekel et al. June 14, 1955 

1. IN A PROCESS FOR THE RECOVERY OF A SUBSTANTIALLY PURE ALCOHOL FRACTION FROM A 20 TO 50 WEIGHT PERCENT AQUEOUS CARBOXYLIC ACID SOAP SOLUTION COMPRISING CARBONYLS AND ALCOHOLS OF THE TYPE FOUND IN THE HYDROCARBON PHASE PRODUCED BY THE FISCHER TROPSCH SYNTHESIS AND CONTAMINATING AMOUNTS OF DISSOLVED HYDROCARBONS, SAID SOAP BEING DERIVED FROM A MIXTURE OF FATTY ACIDS HAVING AN AVERAGE MOLECULAR WEIGHT RANGING FROM ABOUT 85 TO ABOUT 135 WHEREIN SAID SOAP SOLUTION IS CONTACTED WITH A LIQUID LIGHT SATURATED HYDROCARBON HAVING FROM 3 TO 4 CARBON ATOMS, THE IMPROVEMENT WHICH COMPRISES FIRST EXTRACTING SAID SOAP SOLUTION WITH SAID LIGHT BY HYDROCARBON IN A VOLUME RATIO OF LIGHT HYDROCARBON TO SAID SOLUTION OF FROM ABOUT 1:10 TO 1:4 AT A TEMPERATURE RANGING FROM ABOUT 80*F. TO NOT MORE THAN ABOUT 5*F. BELOW THE CRITICAL TEMPERATURE OF SAID LIGHT HYDROCARBON AND AT MINIMUM PRESSURES RANGING FROM ABOUT 25 TO 50 P. S. I. FOR THE C4 HYDROCARBONS TO ABOUT 140 P. S. I. FOR THE C3 HYDROCARBON, SAID EXTRACTION BEING CARRIED OUT IN AN EXTRACTION ZONE OF NOT MORE THAN ABOUT ONE STAGE, THEREAFTER SUBJECTING THE RAFFINATE FROM SAID EXTRACTION, WHICH RAFINNATE IS NOW SUBSTANTIALLY FREE FROM CONTAMINATING HYDROCARBONS, TO A SECOND EXTRACTION STEP IN A 